1. Field of the Invention
The present invention relates to circuits for adjusting the power level of a radio frequency transmitter and more particularly to a detector circuit for power measurement in a power level adjustment system for a radio frequency transmitter.
2. Description of the Background Art
In radio frequency transmission systems, it is usual to adjust the transmitter power level. The power level control means typically includes a detector for providing a voltage proportional to the output voltage of the transmitter power amplifier.
In U.S. Pat. No. 4,602,218 issued Jul. 22, 1986 to Vilmur et al., entitled "Automatic Output Control Circuitry For RF Power Amplifiers With Wide Dynamic Range", automatic power output control circuitry is disclosed in which the magnitude of a radio frequency signal is maintained at one of a plurality of magnitudes selected in response to control signals. The radio frequency signal output from a variable output amplifier is sampled and the sample is further amplified and the dynamic range compressed prior to being rectified. The rectified power magnitude signal, which is nonlinearly related to the radio frequency signal magnitude, is adjusted by an adjustment factor selected by the control signals and employed in varying the output of the variable output amplifier to produce a corresponding radio frequency signal output magnitude.
U.S. Pat. No. 5,109,538 issued Apr. 28, 1992 to Ikonen et al. entitled "Circuitry For Widening The Effective Range Of A Transmitter" describes circuitry for widening the power control range of radio telephone. A radio frequency signal is amplified in a controllable power amplifier. After the amplifier a controllable switch is connected, which, while in a first state, does not substantially attenuate the RF power emitted transmitted from the power amplifier. The first power control range of the transmitter is thus produced. When the switch is in a second state, it directs part of the RF power transmitted from the power amplifier to a resistive element and permits part of the RF power to be transmitted to the output of the transmitter. A second power control range is produced in this manner.
U.S. Pat. No. 3,697,857 issued Oct. 10, 1972 to El-Banna entitled "Power Supply And Control Circuit" discloses a power supply and control circuit for providing a high voltage DC output from a low voltage DC source, i.e., a DC battery, especially useful for solid state transmitters. The source is connected across the input and a second source is connected between one terminal of the first source and a corresponding terminal of the input, the second source being in series aiding relationship to the first source. A transistor is serially connected between the first source and the second source, and a diode is connected across the first source with one electrode between the transistor and the second source and the other electrode at the second terminal of the first source. The diode provides short circuit protection.
In U.S. Pat. No. 4,870,698 issued Sep. 26, 1989 to Katsoyama et al. entitled "Output Power Control Circuit For A Mobile Radio Apparatus" an output power control circuit is described disposed in a casing of a mobile radio apparatus together with an automatic power control circuit and an RF signal amplifier. The output power control circuit applied level control signals to the automatic power control circuit for maintaining the power level of the output RF signal of the RF amplifier at one of a plurality of output power levels corresponding to the level control signals. The output power control circuit has a receiver, a temperature sensing circuit and a logic circuit. The receiver receives RF signals transmitted by a master station and dictates power level setting command signals included in the received RF signal. The temperature sensing circuit detects an internal temperature of the casing and provides a power reduction signal upon detecting that the internal temperature has exceeded a predetermined temperature. The logic circuit receives the power level setting command signal from said receiver, and generates a level control signal for determining an output power level corresponding to the power level setting command signal, and generates a level control signal for determining an output power level which is lower than that specified by the power level setting command signal upon receiving the power reduction signal from the temperature sensing circuit.